This is an ongoing collaborative project suported , in part, by RO1 grants to DRS. Palazzo and Rieder. We previously described (SCIENCE ) the first cell-free system, based on homogenates of surf clam oocytes, that executes centriole duplication. Because centrioles are extremely small (0.25 by 0.5 um), the only way their morphology and replication can be studied is with EM. BOver the past 12 years we have shown that HVEM of serial thick sections greatly facilitates such studies.We are continuing our collaboration and hope to extend our studies to centriole asembly by generating 3_D tomographic reconstructions of the centriole.